Many diseases that afflict animals, including humans, are treated with chemotherapeutic agents. For example, chemotherapeutic agents have proven valuable in the treatment of neoplastic disorders including connective or autoimmune diseases, metabolic disorders, and dermatological diseases, and many of these agents are highly effective and do not suffer from any bioavailability problems.
Proper use of chemotherapeutic agents requires a thorough familiarity with the natural history and pathophysiology of the disease before selecting the chemotherapeutic agent, determining a dose, and undertaking therapy. Each subject must be carefully evaluated, with attention directed toward factors which may potentiate toxicity, such as overt or occult infections, bleeding dyscrasias, poor nutritional status, and severe metabolic disturbances. In addition, the functional condition of certain major organs, such as liver, kidneys, and bone marrow, is extremely important. Therefore, the selection of the appropriate chemotherapeutic agent and devising an effective therapeutic regimen is influenced by the presentation of the subject. Such considerations affect the dosage and type of drug administered.
Unfortunately, not all chemotherapeutics are readily useable. For example, some chemotherapeutic agents are inherently refractory in that animal cells do not readily respond to these agents, while other chemotherapeutics suffer from acquired resistance. For instance, it is well recognised that some subjects on prolonged chemotherapy are forced to change chemotherapeutics as these become less efficacious with time. Moreover, some chemotherapeutics, while not affected by inherent or acquired resistance per se, are not effective in the treatment of certain diseases as they have innate problems with bioavailability. One disease that is frequently affected by both cellular resistance and bioavailability problems is cancer.
Cancer is responsible for one in four deaths in Western society. While the rates of new cases of cancer and deaths with cancer decreased in the United States and Canada between 1990-1994, the data show that 2,604,650 people in the United States died from cancer between 1990-1994, with more men (53%) than women (47%) affected. The most common cancer deaths were due to cancer of the lung (728,641), colon and rectum (285,724), breast (218,786), and prostate (169,943).
Among women, the most common cancers are breast (31%), lung (12%), colon and rectum (12%), uterus (6%), and ovary (4%), with breast and ovarian cancer representing approximately 35% of all cancers found in women. The majority of women diagnosed with these forms of cancer receive a combination of surgical, radiation therapy or chemotherapy.
Chemotherapeutic agents used to treat cancer can be subdivided into several broad categories, including, (1) alkylating agents, such as mechlorethamine, cyclophosphamide, melphalan, uracil mustard, chlorambucil, busulfan, carmustine, lomustine, semustine, streptozoticin, and decrabazine; (2) antimetabolites, such as methotrexate, fluorouracil, fluorodeoxyuridine, cytarabine, azarabine, idoxuridine, mercaptopurine, azathioprine, thioguanine, and adenine arabinoside; (3) natural product derivatives, such as vinblastine, vincristine, dactinomycin, daunorubicin, doxorubicin, mithramycin, taxanes (e.g., paclitaxel) bleomycin, etoposide, teniposide, and mitomycin C; and (4) miscellaneous agents, such as hydroxyurea, procarbezine, mititane, and cisplatinum.
Important cancer chemotherapeutic agents (with the usual effective dosage) to which clinical multidrug-resistance has been observed include vinblastine (0.1 mg per kilogram per week), vincristine (0.01 mg per kilogram per week), etoposide (35 to 50 mg per square meter per day), dactinomycin (0.15 mg per kilogram per day), doxorubicin (500 to 600 mg per square meter per week), daunorubicin (65 to 75 mg per square meter per week), and mithramycin (0.025 mg per kilogram per day).
It is well appreciated by those skilled in the field that, at present, there are no effective means of overcoming cellular resistance to chemotherapeutic agents. More importantly there are no practical means of increasing bioavailability of chemotherapeutics without concomitant increase in toxicity or side effects. Accordingly, there is a requirement for means of overcoming or at least alleviating the problems associated with acquired or inherent cellular resistance as well as means of increasing bioavailability of chemotherapeutics.
The applicant has previously investigated the usefulness of hyaluronan (HA) as a drug delivery vehicle for chemotherapeutics, and found that HA was useful when co-administered with these drugs. International patent application no. PCT/AU00/00004 was filed covering this invention, and is incorporated in its entirety herein by reference. HA, also known as hyaluronic acid, is a naturally occurring polysaccharide comprising linear-chain polymers, which is found ubiquitously throughout the animal kingdom. HA is highly water-soluble, making it an ideal drug delivery vehicle for biological systems.
Subsequent to the filing of International patent application no. PCT/AU00/00004, the applicant surprising found that HA could act as a sole agent. It was found that HA could exert a cytotoxic effect on human breast cancer cells, as well as pre-sensitizing cells so that they became more susceptible to chemotherapeutic agents. The present invention therefore provides methods whereby cells that were, or had become resistant to chemotherapeutic agents could be effectively treated. More importantly, by using the disclosed methods it is possible to decrease the dosages of chemotherapeutic agents without decreasing the efficacy to the subject. The methods of the invention include administering hyaluronan either alone in conjunction with a chemotherapeutic agent.
The present invention is based upon the discovery that hyaluronan, derivatives, analogues, and salts thereof, not only inhibit cells per se, but also allows the safe administration of selected chemotherapeutic agents at standard or lower doses thought to be less effective, to treat subjects including human subjects. In vivo administration of hyaluronan in combination with chemotherapeutic agents also enhances the therapeutic effect of these agents against cells that are refractory, thus preventing the subsequent emergence of multidrug resistance.
Diseased cells such as cancer cells often have more permeable membranes due to an alteration in the membrane potential, or increased receptor status which can alter the regulation of their intracellular molecule transport which can result in cell swelling (Lang et al, 1993). While the applicant does not wish to be bound by any theory they postulate that there are several mechanisms that could explain the cellular effect that HA is exerting both as a sole agent, and as a pre-treatment for therapeutic agents:
1). When HA is bound to CD44, RHAMM and the scavenger receptor bound, the nett negative charge of HA alters the membrane potential of the cell resulting in an increase in cell permeability consequently enabling a greater flux of drug into the diseases cell.
2). When HA is bound to diseased cells such as tumour cells and internalised there could be a hyperosmotic effect resulting in cell lysis.
3). HA could exert oxidative membrane damage resulting in apoptosis.
4). HA internalisation could elevate the mitochondrial membrane potential which could result in cell death or increased drug retention.
Since HA is administered at satuarable levels, there would be a constant internalisation of the glycosaminoglycan which means that any therapeutic agent which is in an equilibrium within the volumetric domain of the HA is co-internalised resulting in a concentrated intracellular release of the drug